This invention relates generally to non-destructive testing and, more particularly, to ultrasound inspection of fabricated components.
Ultrasonic inspection techniques are used in many applications where non-destructive evaluation of a workpiece or component is required. One application of such ultrasonic inspection is in the inspection of gas turbine engine rotors. Such rotors are typically formed from a forging of a material with desired metallurgical properties, for example, Rene-88. In the production of aerospace rotating components, the entire volume of the finished component is required to be inspected ultrasonically. This requires that additional material be present on the forging when it is inspected before machining the finished component. This additional material is referred to as the material envelope and must be equal to or greater than the near surface resolution capability of the ultrasonic inspection process.
The capability to detect signals from near surface targets, such as flaws and/or discontinuities is a critical to quality feature of an ultrasonic inspection process. A near surface target, as used herein, refers to any target of interest positioned closely to either the front or back surface of the inspection sample. The near surface resolution of a given ultrasonic inspection process, as used herein, refers to the minimum distance from the front (or back) surface of the component to a target that produces an ultrasonic signal that meets the requirements of-the inspection process.
From a component cost perspective, it is important to minimize the material envelope. Due to the high raw material costs for aerospace rotating components, even small reductions in material envelope can have a large impact on component cost. However, known systems are limited in the near surface resolution capability that would permit lessened material envelope requirements.